Edgar Filing: ANTIGENICS INC /DE/

Antigenics Inc.

Dated: September 11, 2009

/s/ Shalini Sharp

Shalini Sharp

Chief Financial Officer

Form 424(b)(3)

Filed Pursuant to Rule 424(b)(3) and Rule 424(c)
Registration No. 333-156556

September 11, 2009

PROSPECTUS SUPPLEMENT NO. 17

5,929,212 SHARES OF COMMON STOCK

ANTIGENICS INC.

This prospectus supplement amends the prospectus dated March 18, 2009 (as supplemented on April 15, 2009, April 17, 2009, April 22, 2009, April 27, 2009, May 4, 2009, May 11, 2009, May 27, 2009, June 4, 2009, June 8, 2009, June 9, 2009, June 11, 2009, June 15, 2009, July 7, 2009, July 15, 2009, August 3, 2009, and August 5, 2009) that relates to the issuance of up to 5,929,212 shares of our common stock, par value $0.01 per share (“common stock”), issuable upon the conversion of 5,250 shares of Series B2 Convertible Preferred Stock, par value $0.01 per share (“Series B2 Convertible Preferred Stock”). If the shares of Series B2 Convertible Preferred Stock are converted through payment of cash consideration, if at all, we will receive the cash from such conversion.

This prospectus supplement is being filed to include the information set forth in the Current Report on Form 8-K filed on September 11, 2009, which is set forth below. This prospectus supplement should be read in conjunction with the prospectus dated March 18, 2009, Prospectus Supplement No. 1 dated April 15, 2009, Prospectus Supplement No. 2 dated April 17, 2009, Prospectus Supplement No. 3 dated April 22, 2009, Prospectus Supplement No. 4 dated April 27, 2009, Prospectus Supplement No. 5 dated May 4, 2009, Prospectus Supplement No. 6 dated May 11, 2009, Prospectus Supplement No. 7 dated May 27, 2009, Prospectus Supplement No. 8 dated June 4, 2009, Prospectus Supplement No. 9 dated June 8, 2009, Prospectus Supplement No. 10 dated June 9, 2009, Prospectus Supplement No. 11 dated June 11, 2009, Prospectus Supplement No. 12 dated June 15, 2009, Prospectus Supplement No. 13 dated July 7, 2009, Prospectus Supplement No. 14 dated July 15, 2009, Prospectus Supplement No. 15 dated August 3, 2009, and Prospectus Supplement No. 16 dated August 5, 2009, which are to be delivered with this prospectus supplement.

Our common stock is quoted on The NASDAQ Capital Market (“NASDAQ”) under the ticker symbol “AGEN.” On September 9, 2009, the last reported closing price per share of our common stock was $2.15 per share.

Investing in our securities involves a high degree of risk. Before investing in any of our securities, you should read the discussion of material risks in investing in our common stock. See “Risk Factors” on page 1 of the prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

THE DATE OF THIS PROSPECTUS SUPPLEMENT NO. 17 IS SEPTEMBER 11, 2009

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

The Securities Exchange Act of 1934

September 9, 2009

Date of Report (Date of earliest event reported)

ANTIGENICS INC.

(Exact name of registrant as specified in its charter)

DELAWARE

000-29089

06-1562417

(State or other jurisdiction

of incorporation)

(Commission File Number)

(IRS Employer

Identification No.)

3 Forbes Road

Lexington, MA

02421

(Address of principal executive offices)

(Zip Code)

781-674-4400

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 3.02.

Unregistered Sales of Equity Securities.

On September 9, 2009, Antigenics Inc. (the “Company”) entered into Securities Exchange Agreements (the “Agreements”) with holders of an aggregate principal amount of $1,273,000 of the Company’s 5.25% convertible senior notes due February 2025 (the “Bonds”), to issue 424,330 shares of the Company’s common stock, par value $0.01 (the “Shares”) in exchange for cancellation of the Bonds, including accrued and unpaid interest. The Shares are not registered under the Securities Act of 1933 (the “Act”). The Company issued the Shares in transactions exempt from the registration requirements of the Act by virtue of the exemption provided for in Section 3(a)(9) of the Act for securities exchanged by the issuer with an existing security holder. No commission or other remuneration was paid or given directly or indirectly for soliciting such exchange.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.